Method of allocating a resource in a wireless communication system and device for same

ABSTRACT

In a wireless communication system, when a terminal receives control information from a downlink subframe, which is divided into a Physical Downlink Control Channel (PDCCH) region and a Physical Downlink Shared Channel (PDSCH) region, in a wireless communication system, the receiving of the control information includes: receiving, from a base station, first CFI information indicating the number of Orthogonal Frequency Division Multiplexing (OFDM) symbols available for Physical Downlink Control Channel (PDCCH) transmission; receiving, from the base station, second CFI information indicating start OFDM symbol information available for Physical Downlink Shared Channel (PDSCH) transmission corresponding to an enhanced Physical Downlink Control Channel (E-PDCCH); and receiving the PDSCH from the base station on the basis of the first CFI information or the second CFI information. The PDCCH is placed in the PDCCH region of the downlink subframe, and the E-PDCCH is placed in the PDSCH region of the downlink subframe.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method and apparatus for allocating frequencyresources to new control channels located in a data region of a node ina distributed multi-node system.

BACKGROUND ART

In a current wireless communication environment, the emergence andproliferation of various devices such as Machine-to-Machine (M2M)devices conducting M2M communication, smart phones requiring large-datatransmission, and tablet computers is a driving force behind a veryrapid increase in the amount of data required for a network of awireless communication system. To meet the requirement of a largeramount of data, carrier aggregation and cognitive radio have beendeveloped to efficiently use more frequency bands, and multi-antennatechnology and multi-base station cooperation technology have beendeveloped to increase a data capacity in a limited frequency. Thewireless communication environment is evolving toward more denselypopulated nodes accessible to users. Such a system having denselypopulated nodes may provide higher system performance throughcooperation between nodes. In this scheme, each node conductscooperative communication through a plurality of nodes operating as BaseStations (BSs), Advanced BSs (ABSs), Node Bs, evolved Node Bs (eNBs oreNode Bs), Access Points (APs), antennas, antenna groups, Remote RadioHeads (RRHs), or Remote Radio Units (RRUs).

Further, if one controller manages transmission and reception of allnodes and thus individual nodes act as antenna groups of an eNB, thissystem may be regarded as a Distributed Multi-Node System (DMNS). Theindividual nodes may be allocated separate Node Identifiers (IDs) oroperate as some antennas of a cell without Node IDs.

If the nodes of a DMNS have different cell IDs, this system may beconsidered to be a multi-cell system (e.g. including a macro cell, afemto cell, and a pico cell). If the multiple cells formed by therespective nodes are overlaid according to their coverage, this networkis referred to as a multi-tier network.

Various types of BSs may be used as nodes irrespective of theirappellations. That is, a BS, a Node B, an eNB, a Picocell eNB (PeNB), aHome eNB (HeNB), an RRH, an RRU, a relay, a repeater, etc. may act as anode. At least one antenna is installed in one node. The antenna may beany of a physical antenna, an antenna port, a virtual antenna, and anantenna group. A node may also be referred to as a point.

Although a node typically refers to an antenna group spaced by apredetermined distance or more, the node may mean an arbitrary antennagroup irrespective of the distance. For example, an eNB may control anode having H-pol antennas and a node having V-pol antennas. In thepresent disclosure, the term antenna may be replaced with the termsphysical antenna, antenna port, virtual antenna, antenna group, etc.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ona method and apparatus for efficiently allocating resources to aphysical channel in a wireless communication system. Another object ofthe present invention lies on a channel format, a signal process, and anapparatus for efficiently transmitting control information. A furtherobject of the present invention lies on a method and apparatus forefficiently allocating resources in which control information is to betransmitted.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present invention are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present invention could achieve will be more clearlyunderstood from the following detailed description.

Technical Solution

The object of the present invention can be achieved by providing amethod for receiving control information in a downlink subframe dividedinto a Physical Downlink Control Channel (PDCCH) region and a PhysicalDownlink Shared Channel (PDSCH) region at a User Equipment (UE) in awireless communication system, including receiving, from a Base Station(BS), first Control Format Indicator (CFI) information indicating thenumber of Orthogonal Frequency Division Multiplexing (OFDM) symbolsavailable for transmission of a PDCCH, receiving, from the BS, secondCFI information indicating a starting OFDM symbol available fortransmission of a PDSCH corresponding to an Enhanced PDCCH (E-PDCCH),and receiving a PDSCH based on the first CFI information or the secondCFI information from the BS. The PDCCH is positioned in the PDCCH regionof the downlink subframe and the E-PDCCH is positioned in the PDSCHregion of the downlink subframe.

In another aspect of the present invention, provided herein is a methodfor transmitting control information in a downlink subframe divided intoa PDCCH region and a PDSCH region at a BS in a wireless communicationsystem, including transmitting, to a UE, first CFI informationindicating the number of OFDM symbols available for transmission of aPDCCH, transmitting, to the UE, second CFI information indicating astarting OFDM symbol available for transmission of a PDSCH correspondingto an E-PDCCH, and transmitting a PDSCH based on the first CFIinformation or the second CFI information to the UE. The PDCCH islocated in a PDCCH region of the downlink subframe and the E-PDCCH islocated in a PDSCH region of the downlink subframe.

In another aspect of the present invention, provided herein is a UE forreceiving control information in a downlink subframe divided into aPDCCH region and a PDSCH region in a wireless communication system,including a Radio Frequency (RF) unit, and a processor. The processor isconfigured to control the RF unit to receive, from a BS, first CFIinformation indicating the number of OFDM symbols available fortransmission of a PDCCH, to control the RF unit to receive, from the BS,second CFI information indicating a starting OFDM symbol available fortransmission of a PDSCH corresponding to an E-PDCCH, and to control theRF unit to receive a PDSCH based on the first CFI information or thesecond CFI information from the BS. The PDCCH is located in a PDCCHregion of the downlink subframe and the E-PDCCH is located in a PDSCHregion of the downlink subframe.

In another aspect of the present invention, provided herein is a BS fortransmitting control information in a downlink subframe divided into aPDCCH region and a PDSCH region in a wireless communication system,including an RF unit and a processor. The processor is configured tocontrol the RF unit to transmit, to a UE, first CFI informationindicating the number of OFDM symbols available for transmission of aPDCCH, to control the RF unit to transmit, to the UE, second CFIinformation indicating a starting OFDM symbol available for transmissionof a PDSCH corresponding to an E-PDCCH, and to control the RF unit totransmit a PDSCH based on the first CFI information or the second CFIinformation to the UE. The PDCCH is located in a PDCCH region of thedownlink subframe and the E-PDCCH is located in a PDSCH region of thedownlink subframe.

The first CFI information may be transmitted from the BS by RadioResource Control (RRC) signaling and the second CFI information may bereceived from the BS by RRC signaling or on the E-PDCCH.

The PDSCH may be received from the BS only based on the first CFIinformation in a subframe carrying a control channel for an idle UE.

Advantageous Effects

According to the embodiments of the present invention, resources may beefficiently allocated to a physical channel in a wireless communicationsystem, preferably a Distributed Multi-Node System (DMNS).

It will be appreciated by persons skilled in the art that that theeffects that can be achieved through the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 illustrates an exemplary Distributed Antenna System (DAS)configuration to which the present invention is applied;

FIG. 2 illustrates an exemplary control region in which a PhysicalDownlink Control Channel (PDCCH) may be transmitted in a 3^(rd)Generation Partnership Project (3GPP) Long Term Evolution(LTE)/LTE-Advanced (LTE-A) system;

FIG. 3 illustrates a structure of an uplink subframe in a 3GPP system;

FIG. 4 illustrates control channels allocated to a downlink subframe;

FIG. 5 illustrates an exemplary mapping relationship between PhysicalControl Format Indicator Channels (PCFICHs) and resources according tocell Identifiers (IDs);

FIG. 6 illustrates an exemplary resource allocation by an EnhancedPhysical Downlink Control Channel (E-PDCCH);

FIG. 7 illustrates an exemplary Relay PDCCH (R-PDCCH) allocationstructure for a relay;

FIG. 8 illustrates an operation for transmitting a Physical DownlinkShared Channel (PDSCH) in a part of a PDCCH region according to aControl Format Indicator (CFI) and a second CFI (a CFI2) according to anembodiment of the present invention;

FIGS. 9 and 10 illustrate mapping of a PDSCH to Resource Elements (REs)according to an embodiment of the present invention; and

FIG. 11 illustrates a Base Station (BS) and a User Equipment (UE) thatare applicable to the present invention.

BEST MODE

Reference will now be made in detail to the preferred embodiments of thepresent invention with reference to the accompanying drawings. Thedetailed description, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present invention, rather than to show the only embodiments that canbe implemented according to the invention. The following detaileddescription includes specific details in order to provide a thoroughunderstanding of the present invention. However, it will be apparent tothose skilled in the art that the present invention may be practicedwithout such specific details. For example, the following description isgiven in the context of a 3^(rd) Generation Partnership Project LongTerm Evolution (3GPP LTE) system or an Institute of Electrical andElectronics Engineers (IEEE) 802.16m system as a mobile communicationsystem. However, the present invention is applicable to other mobilecommunication systems except for features inherent to the 3GPP LTEsystem or the IEEE 802.16m system.

In some instances, known structures and devices are omitted or are shownin block diagram form, focusing on important features of the structuresand devices, so as not to obscure the concept of the invention. The samereference numbers will be used throughout this specification to refer tothe same parts.

A wireless communication system to which the present invention isapplicable includes at least one Base Station (BS). Each BS provides acommunication service to a User Equipment (UE) within a specificgeographical area (generally called a cell). The UE is fixed or mobile.The UE is a device that transmits and receives user data and/or controlinformation by communicating with a BS. The term ‘UE’ may be replacedwith ‘terminal equipment’, ‘Mobile Station (MS)’, ‘Mobile Terminal(MT)’, ‘User Terminal (UT)’, ‘Subscriber Station (SS)’, ‘wirelessdevice’, ‘Personal Digital Assistant (PDA)’, ‘wireless modem’, ‘handhelddevice’, etc. A BS is typically a fixed station that communicates with aUE and/or another BS. The BS exchanges data and control information witha UE and another BS. The term ‘BS’ may be replaced with ‘evolved-Node B(eNB or eNode B)’, ‘Base Transceiver System (BTS)’, ‘Access Point (AP)’,‘Processing Server (PS)’, etc.

A cell area to which a BS provides a service may be divided into aplurality of smaller areas to improve system performance. Each smallerarea may be referred to as a sector or a segment. While a CellIdentifier (ID) (Cell_ID or IDCell) is allocated from the perspective ofa whole system, a sector ID or a segment ID is allocated from theperspective of a cell area to which a BS provides a service. UEs aregenerally distributed in a wireless communication system and are fixedor mobile. Each UE may communicate with one or more BSs at a specifictime point on an UpLink (UL) and/or a DownLink (DL).

The present invention is applicable to various kinds of multi-nodesystems. For example, embodiments of the present invention may beapplicable to a Distributed Antenna System (DAS), a macro node havinglow-power Remote Radio Heads (RRHs), a multi-BS cooperative system, apico-cell/femto-cell cooperative system, or a combination thereof. In amulti-node system, one or more BSs connected to a plurality of nodes maysimultaneously transmit signals to or receive signals from a UE throughcooperation.

A DAS conducts communication using a plurality of distributed antennasconnected to a BS or a BS Controller (BSC) by a cable or a dedicatedline, which manages a plurality of antennas apart from each other by apredetermined interval within a geographical area (or a cell). In theDAS, each antenna or each antenna group may be a node in the multi-nodesystem of the present invention and each antenna may operate as a subsetof antennas in the BS or the BSC. That is, the DAS is a kind ofmulti-node system and distributed antennas or a distributed antennagroup is a kind of node in a multi-antenna system. The DAS is differentfrom a Centralized Antenna System (CAS) in that a plurality of antennasare apart from each other by a predetermined distance in the former anda plurality of antennas are concentrated at the center of a cell in thelatter. In addition, the DAS is different from a femto-cell/pico-cellcooperative system in that all antennas located within a cell aremanaged by a BS or a BSC at the center of the cell, not by distributedantennas or a distributed antenna group in the DAS. In addition, the DASis different from a relay system or an ad-hoc network in thatdistributed antennas are interconnected by a cable or a dedicated linein the former, whereas a BS is connected wirelessly to a Relay Station(RS) in the latter. The DAS is different from a repeater in that adistributed antenna or a distributed antenna group transmits, to a UElocated near to the antenna or the antenna group, a different signalfrom a signal from another distributed antenna or another distributedantenna group by a command received from a BS or a BSC in the former,whereas a signal is simply amplified and forwarded in the latter.

In a multi-BS cooperative system or a femto-cell/pico-cell cooperativesystem, each node operates as an independent BS and cooperates withother nodes. Therefore, each BS of the multi-BS cooperative system orthe femto-cell/pico-cell cooperative system may be a node of themulti-node system according to the present invention. Multiple nodes areinterconnected through a backbone network or the like and perform acooperative transmission/reception by performing scheduling and/orhandover jointly in the multi-BS cooperative system or thefemto-cell/pico-cell cooperative system. Such a system in which aplurality of BSs participate in cooperative transmission is referred toas a Coordinated Multi-Point (CoMP) system.

Various types of multi-node systems such as a DAS, a macro node havinglow-power RRHs, a multi-BS cooperative system, and afemto-cell/pico-cell cooperative system are different from one another.However, these multi-node systems are different from single-node systems(e.g., a Centralized Antenna System (CAS), a conventional Multiple InputMultiple Output (MIMO) system, a conventional relay system, aconventional repeater system, etc.). Since a plurality of nodesparticipate in providing a communication service to a UE by cooperation,embodiments of the present invention are applicable to any of thesemulti-node systems. For the convenience of description, the presentinvention will be described mainly in the context of a DAS. However,this is purely exemplary and thus it is to be understood that since anantenna or an antenna group of the DAS may correspond to a node ofanother multi-node system and a BS of the DAS may correspond to one ormore cooperative BSs of another multi-node system, the present inventionis applicable to other multi-node systems in the same manner.

FIG. 1 illustrates an exemplary DAS structure to which the presentinvention is applied. Specifically, an exemplary system structure isshown, in which a DAS is applied to a conventional CAS using cell-basedmultiple antennas.

Referring to FIG. 1, a plurality of Centralized Antennas (CAs) havingsimilar effects such as similar path losses due to a narrow antennaspacing relative to a cell radius may be located in an area near to a BSaccording to an embodiment of the present invention. A plurality ofDistributed Antennas (DAs) each having a different effect such as adifferent path loss due to a wider antenna spacing than the CAs may bedistributed apart from the cell area by a predetermined distance orfarther.

A DA includes one or more antennas connected to the BS by one cable. Theterm DA is interchangeable with the terms DA antenna node or antennanode in the same meaning. One or more DAs form one DA group, thusforming a DA zone.

A DA group includes one or more DAs. The DA group may be configureddynamically according to the location or reception state of a UE or maybe configured to include a fixed maximum number of antennas used forMIMO. A DA group may also be called an antenna group. A DA zone isdefined as a range in which the antennas of a DA group may transmit orreceive signals. A cell area illustrated in FIG. 1 includes n DA zones.A UE belonging to a DA zone may communicate with one or more DAs of theDA zone and the BS may increase a transmission rate by transmitting asignal to the UE of the DA zone using both a DA and a CA.

FIG. 1 illustrates a conventional CAS structure using multiple antennasto which a DAS is added so that a BS and a UE may use the DAS. While CAsand DAs are shown as located separately for the simplicity ofdescription, the present invention is not limited to the specificlocations of the CAs and the DAs, and the CAs and the DAs may bepositioned in various manners depending on implementation.

A cell area to which a BS provides a service may be divided into aplurality of smaller areas to improve system performance. Each smallerarea may be referred to as a sector or a segment. While a cell ID(Cell_ID or IDCell) is assigned from the perspective of a whole system,a sector ID or a segment ID is assigned from the perspective of a cellarea to which a BS provides a service. UEs may be distributed across awireless communication system and may be fixed or mobile. Each UE maycommunicate with one or more BSs on a UL and a DL.

FIG. 1 illustrates a CAS including a DAS in the conventionalmulti-antenna CAS structure, so that a BS and a UE may use the DAS.While CAs and DAs are shown as located separately for the simplicity ofdescription, the present invention is not limited to the specificlocations of the CAs and the DAs illustrated in FIG. 1, and the CAs andthe DAs may be positioned in various manners depending onimplementation.

AS illustrated in FIG. 1, limited antennas or antenna nodes may supporteach UE. Particularly for DL data transmission, different data may betransmitted to different UEs in the same time and frequency resourcesthrough different antennas or antenna nodes. This may be regarded as akind of MU-MIMO operation in which a different data stream istransmitted through each antenna or antenna node by selecting theantenna or antenna node.

In the present invention, each antenna or antenna node may be an antennaport. An antenna port is a logical antenna configured with one or morephysical transmission antenna elements. In addition, each antenna orantenna node may be a virtual antenna in the present invention. Inbeamforming, a signal transmitted by a precoded beam may be consideredto be transmitted through one antenna and the antenna that transmits theprecoded beam is called a virtual antenna. Each antenna or antenna nodemay be identified by a reference signal (or a pilot signal) in thepresent invention. An antenna group including one or more antennas thattransmit the same reference signal or the same pilot signal refers toone or more antenna sets that transmit the same reference signal or thesame pilot signal. That is, each antenna or antenna node of the presentinvention may be interpreted as a physical antenna or a set of physicalantennas, an antenna port, a virtual antenna, or an antenna identifiedby a reference signal/pilot signal. In embodiments of the presentinvention described below, an antenna or an antenna node may refer toany of a physical antenna, a set of physical antennas, an antenna port,a virtual antenna, or an antenna identified by a reference signal/pilotsignal. Hereinbelow, a physical antenna, a set of physical antennas, anantenna port, a virtual antenna, and an antenna identified by areference signal/pilot signal will be referred to as an antenna or anantenna node.

Referring to FIG. 2, a radio frame is 10 ms (32700 Ts) long, including10 equal-sized subframes in the 3GPP LTE/LTE-A system. Each subframe is1 ms long and divided into two slots, each having a length of 5 ms.Herein Ts represents a sampling time determined by Ts=1/(2048×15 kHz). Aslot includes a plurality of OFDMA symbols in the time domain and aplurality of Resource Blocks (RBs) in the frequency domain. An RBincludes a plurality of subcarriers in the frequency domain. Dependingon multiple access schemes, an OFDMA symbol is referred to as an OFDMAsymbol, an SC-FDMA symbol, etc. The number of OFDMA symbols in one slotmay vary according to a channel bandwidth and a Cyclic Prefix (CP)length. For example, one slot includes 7 OFDMA symbols in a normal CPcase, whereas one slot includes 6 OFDMA symbols in an extended CP case.While a subframe is shown in FIG. 2 as including 7 OFDMA symbols in eachslot for the convenience of description, embodiments of the presentinvention as described below may be applied to other types of subframesin the same manner. In the 3GPP LTE/LTE-A system, a resource unitdefined by one OFDMA symbol and one subcarrier is called a ResourceElement (RE).

In the 3GPP LTE/LTE-A system, each subframe is divided into a controlregion and a data region. The control region includes one or more OFDMAsymbols starting from the first OFDMA symbol. The size of the controlregion may be set independently in each subframe. A Physical DownlinkControl Channel (PDCCH), a Physical Control Format Indicator Channel(PCFICH), and a Physical Hybrid automatic repeat request IndicatorChannel (PHICH) may be allocated to the control region.

As illustrated in FIG. 2, control information is transmitted to a UE inpredetermined time and frequency resources from among radio resources. Acontrol channel delivers control information about a UE (or UEs),inclusive of MAP information. Each UE searches for a control channelamong control channels transmitted by an eNB and receives the detectedcontrol channel. As more UEs are located within a cell, the proportionof resources occupied by control channels is increased. If Machine toMachine (M2M) communication and a DAS get popular, the number of UEswithin a cell may further be increased. Accordingly, control channelsmay be bulky to support such UEs. That is, the number of OFDMA symbolsoccupied by control channels in a subframe and/or the number ofsubcarriers occupied by control channels in the subframe may beincreased. Therefore, the present invention provides methods forefficiently using control channels by utilizing the characteristics of aDAS.

According to the current CAS-based communication standards, all antennasof a BS transmit control channels for all UEs (e.g. a MAP, anAdvance-MAP (A-MAP), a PDCCH, etc.) in the control region. Each UEshould acquire control information directed to the UE by processing thecontrol region being a common area preset for control informationtransmission in order to acquire control information such as informationabout an antenna node allocated to the UE and DL/UL resource allocationinformation. For example, the UE should acquire its control informationfrom among signals transmitted in the control region by applying ascheme such as blind decoding.

If the antennas transmit control information for all UEs in the samecontrol region according to the current communication standards, theantennas are easily implemented since all antennas transmit the samesignal in the control region. However, if the size of controlinformation to be transmitted increases due to factors including theincrease of UEs to be covered by a BS, a Multi User MIMO (MU-MIMO)operation, additional control information for a DAS (e.g. informationabout antenna nodes allocated to a UE), etc., the sizes or number ofcontrol channels is increased, thereby making it difficult to transmitall control information in the conventional control region.

FIG. 3 illustrates a UL subframe structure used in a 3GPP system.

Referring to FIG. 3, a basic unit for LTE UL transmission, that is, a1-ms subframe 500 includes two 0.5-ms slots 501. In a normal CP case,each slot includes 7 symbols 502 each corresponding to one SC-FDMAsymbol. An RB 503 is a resource allocation unit including 12 subcarriersin frequency by one slot in time. The LTE UL subframe is largely dividedinto a data region 504 and a control region 505. The data region 504 iscommunication resources used to transmit data such as voice and packetsto each UE. A Physical Uplink Shared Channel (PDSCH) is allocated to thedata region 504. The control region 505 is communication resources for aUE used to transmit a DL channel quality report, anACKnowledgement/Negative ACKnowledgement (ACK/NACK) for a DL signal, aUL scheduling request, etc. A Physical Uplink Control Channel (PUCCH) isallocated to the control region 505. A Sounding Reference Signal (SRS)is transmitted in the last SC-FDMA symbol of a subframe on the time axisin a data transmission band on the frequency axis. SRSs transmitted inthe last SC-FDMA symbol of the same subframe from a plurality of UEs maybe distinguished by frequency positions/sequences.

Now, RB mapping will be described. Physical Resource Blocks (PRBs) andVirtual Resource Blocks (VRBs) are defined. A PRB is configured asillustrated in FIG. 3. That is, a PRB is defined as a predeterminednumber of consecutive Orthogonal Frequency Division Multiplexing (OFDM)symbols in the time domain by a predetermined number of consecutivesubcarriers in the frequency domain. PRBs are numbered, starting from 0to a predetermined index in the frequency domain. A relationship betweenPRB indexes and REs in a slot is determined by Equation 1.

$\begin{matrix}{n_{PRB} = {{*\frac{k}{N_{SC}^{RB}}} +}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

In Equation 1, k is the index of a subcarrier and N^(RB) _(SC) is thenumber of subcarriers included in one RB.

A VRB and a PRB are of the same size. VRBs are classified into LocalizedVRB (LVRB) and Distributed VRB (DVRB). A pair of RBs are allocatedacross two slots of a subframe, along with a VRB index 0 irrespective ofthe type of a VRB.

FIG. 4 illustrates an exemplary mapping relationship between cell IDsand PCFICH resources.

Referring to FIG. 4, a PHICH is a physical HARQ indicator channelcarrying an HARQ ACK/NACK for a UL transmission. The PHICH includesthree RE Groups (REGs) and is scrambled cell-specifically. The ACK/NACKis indicated in 1 bit, spread with a Spreading Factor (SF) of 4, andrepeated three times. A plurality of PHICHs may be mapped to the sameresources. A PHICH is modulated in Binary Phase Shift Keying (BPSK).

A PDCCH is a physical downlink control channel allocated to the first nOFDM symbols of a subframe. Herein, n is 1 or a larger integer indicatedby a PCFICH. The PDCCH is allocated in units of a CCE and one CCEincludes 9 REGs. The PDCCH delivers resource allocation informationabout transport channels, Paging Channel (PCH) and Downlink SharedChannel (DL-SCH), a UL scheduling grant, HARQ information, etc. The PCHand the DL-SCH are transmitted on a PDSCH. Accordingly, a BS and a UEgenerally transmit and receive data on a PDSCH except for a specificcontrol signal or specific service data. The PDCCH specifies how UEs aresupposed to receive PDSCH data and decode the PDSCH data. For example,if the Cyclic Redundancy Check (CRC) of a specific PDCCH is masked withRadio Network temporary Identify (RNTI) “A” and the PDCCH deliversinformation about data which is to be transmitted in radio resources(e.g. frequency position) “B” based on transmission format information(e.g. a transport block size, a modulation scheme, coding information,etc.) “C” in a specific subframe, one or more UEs within a cell monitorPDCCHs using their RNTI information. If there are one or more UEs havingRNTI “A”, the UEs receive the PDCCH and receive a PDSCH indicated by “B”and “C” based on the information of the received PDCCH.

FIG. 5 illustrates control channels allocated to a DL subframe. In a3GPP Rel-11 or higher-version release system, introduction of amulti-node system having a plurality of access nodes in a cell wasdetermined to improve performance (herein, the multi-node systemincludes a DAS, an RRH, a multi-node system, etc. and hereinbelow, theterm RRH is used representatively). A variety of MIMO schemes andcooperative communication schemes that have been already developed orthat are applicable in the future are under standardization forapplication to a multi-node environment. Basically, it is expected thatlink quality will be improved since various communication schemes suchas cooperation schemes on a UE/BS basis are enabled due to theintroduction of RRHs. However, there exists a pressing need forintroducing a new control channel to apply the afore-described variousMIMO schemes and cooperative communication schemes to the multi-nodeenvironment. To meet the requirement of a new control channel, anRRH-PDCCH, an x-PDCCH, or an E-PDCCH (hereinafter, collectively referredto as an E-PDCCH) has been discussed and it is considered thattransmission of the E-PDCCH in a data region (a PDSCH region) is betterthan in a control region (a PDCCH region). Eventually, the E-PDCCHdelivers control information about a node to each UE, thus overcomingthe shortage of a legacy PDCCH region.

A legacy PDCCH is transmitted in a predetermined region by transmitdiversity, without applying various schemes used for a PDSCH, such asbeamforming, MU-MIMO, best band selection, etc. to the PDCCH. Therefore,the PDCCH behaves as a bottleneck of system performance, thus requiringimprovement. To improve system performance, the introduction of RRHs isunder discussion. In this context, there is a need for a new PDCCH toovercome lack of a PDCCH capacity in case RRHs have the same cell ID.The new PDCCH is called an E-PDCCH distinguishably from the legacyPDCCH. The present invention will be described on the assumption that anE-PDCCH is located in a PDSCH region. That is, an E-PDCCH and a PDSCHcorresponding to the E-PDCCH are characterized by a structure fortransmitting control information in the data region of an existingsubframe, relative to a conventional structure for transmitting controlinformation in the control region of the subframe.

Referring to FIG. 5, a subframe includes 14 OFDM symbols. The first 3OFDM symbols of the subframe are allocated as a control region and theremaining 11 OFDM symbols are allocated as a data region. In FIG. 5, R1,R2, R3, and R4 represent Common Reference Signals (CRSs) for antenna 0,antenna 1, antenna 2, and antenna 3, respectively. The CRSs are fixed toa predetermined pattern in a subframe irrespective of the control regionand the data region. A control channel is allocated to resources exceptfor CRS resources in the control region and a traffic channel is alsoallocated to resources except for CRS resources in the data region.Control channels allocated to the control region are a PCFICH, a PHICH,a PDCCH, etc.

The PCFICH is a physical control format indicator channel indicating thenumber of OFDM symbols used for PDCCHs in each subframe to UEs. ThePCFICH resides in the first OFDM symbol of a subframe. The PCFICHoccupies 4 REGs which are distributed across the control regionaccording to a cell ID. One REG includes 4 REs. The structure of an REGhas been described before with reference to FIG. 4. The PCFICH indicatesa value of 1, 2, or 3 and is modulated in 16-ary Quadrature Phase ShiftKeying (16QAM).

FIG. 6 illustrates an exemplary resource allocation by an E-PDCCH.

Referring to FIG. 6, the E-PDCCH may be allocated to a part of a PDSCHregion in which data is generally transmitted. A UE should perform blinddecoding to detect an E-PDCCH directed to the UE. Minimum informationabout an area in which to detect the E-PDCCH may be signaled by newlydefining a PDCCH or a PCFICH in advance. While the E-PDCCH performs thesame scheduling function (PDSCH and PUSCH control) as the legacy PDCCH,the number of blind decodings is increased with more E-PDCCHs allocatedto the PDSCH region due to the increase of UEs accessing RRHs and thusUE complexity may be increased.

FIG. 7 illustrates an R-PDCCH allocation structure for a relay in aFrequency Division Duplexing (FDD) system. As a specific E-PDCCHallocation scheme, a conventional R-PDCCH structure may be reused. Thatis, an E-PDCCH is configured like an R-PDCCH. This scheme reuses analready existing structure, thus having a relatively small impact on theexisting standard. In regards to the conventional R-PDCCH, only a DLgrant is allocated in a first slot of an existing RB and a UL grant or adata PDSCH may be allocated in a second slot of the existing RB.However, a shortcoming with the conventional R-PDCCH is that the DLgrant should be decoded first. Herein, the R-PDCCH is allocated to REsexcept for a PDCCH region, CRSs, and Demodulation Reference Signals(DMRSs). As illustrated in [Table 1], all of the DMRSs and CRSs may beused to decode the R-PDCCH. If the DMRSs are used, port 7 and aScrambling ID (SCID) of 0 are used. On the other hand, if the CRSs areused, port 0 is used only for one PBCH transmission antenna. For twoPBCH transmission antennas and four PBCH transmission antennas, transmitdiversity mode is set, and ports 0 and 1 and ports 0 to 3 are used,respectively.

TABLE 1 Transmission Transmission scheme of PDSCH mode DCI formatcorresponding to R-PDCCH Mode 8 DCI format 1A If the R-PDCCH isdemodulated based on UE-specific reference signals: Single antenna port;port 7 and is used. If the R-PDCCH is demodulated based on cell-specificreference signals: If the number of PBCH antenna ports is one:Single-antenna port, port 0 is used Otherwise Transmit diversity is usedDCI format 2B Dual layer transmission, port 7 and 8; or single-antennaport, port 7 or 8 Mode 9 DCI format 1A If the R-PDCCH is demodulatedbased on UE-specific reference signals: Single antenna port; port 7 andis used. If the R-PDCCH is demodulated based on cell-specific referencesignals: If the number of PBCH antenna ports is one: Single-antennaport, port 0 is used Otherwise Transmit diversity is used DCI format 2CUp to 4 layer transmission, ports 7-10

In the R-PDCCH structure, a DL grant and a UL grant are allocated to afirst slot and a second slot, respectively and a control channel isallocated to the first slot. That is, the R-PDCCH being a downlinkcontrol channel has a pure Frequency Division Multiplexing (FDM)structure in that it is allocated only to the first slot. In contrast,allocation of an E-PDCCH in a full FDM structure, not limited to oneslot, is under discussion.

In a legacy system, the starting position of a PDSCH in each cell may bedifferent according to the PDCCH region size of the cell and a UE maydetermine the PDCCH region size by higher-layer signaling or by readinga Control Format Indicator (CFI) in a PCFICH. However, a UE of an RRHmay receive a PDSCH in a part or all of resources of a PDCCH region in acell including a macro eNB and RRHs. This resource management method ispossible when no UE that should receive a PDCCH exists within RRHcoverage.

Accordingly, the present invention proposes the following signalingrequired for PDSCH reception in a PDCCH region.

For application to the multi-node environment, there exists a pressingneed for introducing a new control channel. Thus, a method forovercoming lack of a PDCCH capacity is proposed to enable transmissionof control information about a node to each UE. In this context, thepresent invention is intended to overcome the problem of havingdifficulty in allocating a control channel region for each UE in a PDCCHregion, in consideration of the distribution of legacy UEs conforming tothe existing 3GPP LTE/LTE-A standard. In view of the lack of the PDCCHregion, an E-PDCCH is allocated in the PDSCH region. Since an E-PDCCHregion applied to each RRH moves to the PDSCH region, controlinformation allocated to the PDCCH region is reduced. Accordingly, thefollowing methods are proposed to allocate a PDSCH to a part of thePDCCH region according to a conventional CFI and thus utilize a widerPDSCH region.

In a first method, resource allocation information about a PDSCH regionmay be received by using a conventional CFI and receiving an additionalCFI (CFI2). While the conventional CFI may be transmitted on a PCFICH,CFI2 for PDSCH transmission may be signaled additionally.

FIG. 8 illustrates an operation for transmitting a PDSCH in a part of aPDCCH region according to a CFI and CFI2 according to an embodiment ofthe present invention.

Referring to FIG. 8, a UE receives a CFI (CFI2) independent of a CFI ofa PCFICH. A CFI indicating the number of OFDM symbols available forPDCCH transmission may still be used, or CFI2 indicating informationabout the start of OFDM symbols available for PDSCH transmissioncorresponding to an E-PDCCH may be configured separately.

A legacy UE receives the CFI indicating the number of OFDM symbolsavailable for PDCCH transmission in the first symbol of a subframe. Inother words, the CFI means information about the starting OFDM symbol ofa PDSCH to the legacy UE.

For example, if CFI is ‘1’, this means that ‘a PDSCH starts in a secondOFDM symbol’ and if CFI is ‘2’, this means that ‘a PDSCH starts in athird OFDM symbol’. Accordingly, to receive a PDSCH, a legacy UE shouldknow a CFI.

However, to receive a PDSCH in a PDCCH region as proposed in the presentinvention, a UE should receive CFI2 separately from a CFI. CFI2 is aparameter that determines the starting OFDM symbol of the PDSCH. CFI2represents the starting OFDM symbol of the PDSCH directly or the span ofDCI in the PDCCH region, reduced by the PDSCH. That is, CFI2 means thenumber of reduced OFDM symbols relative to the span of DCI representedby the CFI. Thus, the CFI may not indicate the starting OFDM symbol of aPDSCH depending whether the CFI is identical to CFI2.

CFI2 may be configured independently of the CFI, rather than CFI2 isconfigured to indicate the number of OFDM symbols decreased from thespan of DCI represented by the CFI. Therefore, a starting OFDM symbolindicated by CFI2 may be the first OFDM symbol in an extreme case or anOFDM symbol earlier than an OFDM symbol indicated by the CFI. That is,the starting OFDM symbol available for PDSCH transmission correspondingto an E-PDCCH may be positioned before an OFDM symbol indicated by theCFI. For example, the CFI may indicate the third OFDM symbol and CFI2may indicate the first OFDM symbol. Therefore, CFI2 may indicate astarting OFDM symbol freely according to a system determination,independently of the conventional CFI. Thus the starting OFDM symbol maybe even the first OFDM symbol.

Therefore, the UE may receive one or both of the CFI and CFI2. If the UEreads a control channel in the PDCCH region and an E-PDCCH, the UEshould receive both a CFI indicating the number of OFDM symbolsavailable for PDCCH transmission and CFI2 indicating the number of OFDMsymbols available for PDSCH transmission corresponding to the E-PDCCH.Or even though the UE reads only the E-PDCCH, if the starting OFDMsymbol of the E-PDCCH changes according to the size of the PDCCH region,the UE should receive the CFI and CFI2 because CFI2 represents thedecreased number of symbols with respect to the CFI. On the other hand,if the UE reads only an E-PDCCH having a fixed starting OFDM symbolwithout reading information in the PDCCH region, the UE may receive onlyCFI2. Herein, CFI2 represents a smaller OFDM symbol index than the CFI.That is, the lack of the PDCCH region may be overcome by allocating aPDSCH to the PDCCH region using CFI2. If a PDSCH is allocated to thePDCCH region, all antennas of an eNB transmit control channels for allUEs within the cell of the eNB in the PDCCH region according to thecurrent CAS-based communication standards, as illustrated in FIG. 1.According to the present invention, a PDSCH may be allocated to thePDCCH region being a control channel region. In this case, controlinformation for a UE other than an RRH UE allocated to the PDCCH region,for example, an idle UE, or general control information may be lost dueto interference from PDSCH transmission corresponding to an E-PDCCH.However, the eNB may transmit DMRSs of control information and each UEmay reduce the impact of beamforming from the eNB by controlling a beamgain according to precoding. That is, the impact of beamforming causedby other antennas may be reduced by controlling a beam gain using aconvolutional code. In addition, even though a PDSCH is allocated to apart of the PDCCH region, the PDSCH allocation to the PDCCH region doesnot matter much because only one or two symbols of 12 symbols in thePDCCH region are affected.

Accordingly, the present invention provides a method for determining aPDSCH region according to a CFI and CFI2 and receiving a PDSCH from aneNB based on first CFI information and second CFI information.

In the present invention, CFI2 may be transmitted to a UE largely in twomethods: a CFI2 transmission method by RRC signaling and a method forinserting a CFI2 field in the contents of an E-PDCCH. The method fortransmitting CFI2 to a UE by higher-layer signaling does not requireadding or changing of a parameter. On the other hand, the method forinserting a CFI2 field in the contents of an E-PDCCH may immediatelyreflect a dynamic change of a PDCCH region or a PDSCH region for a UE.Or CFI2 may have the same value as a CFI transmitted on a legacy PCFICH.If the CFI has a fixed value, for example, the starting symbol of aPDSCH corresponding to an E-PDCCH is fixed, the CFI2 field may beinserted in the contents of the E-PDCCH.

In a second method, an environment in which a PDSCH is transmitted in aPDCCH region is specified according to a CFI and CFI2. That is, a rangeto which the first method is applicable is specified.

Among 10 subframes of one frame, subframe 0 to subframe 9, there aresome subframes characterized by transmission of a control channel in aPDCCH region for a UE whose position is not detected. For example,subframes 0, 4, 5, and 9 are used to transmit a paging channel.Information about the paging channel is transmitted on a data channeland common information is transmitted in a common search space. In thepresent invention, a control signal for each UE is scrambled with oneCell-Radio Network temporary Identity (C-RNTI) and transmitted in aPDCCH region on the assumption that each UE has the same cell ID. Inthis case, the first method is not implemented to protect the controlsignal for the UE using the paging channel. That is, the eNB uses onlythe conventional CFI not to change the PDCCH region, without allocatinga PDSCH region for data transmission according to CFI2. Or the UEacquires allocated RE information using only the CFI, ignoring CFI2. TheUE receiving the paging channel is not located because it is in idlemode. Thus, PDSCHs for other UEs may not be transmitted in the PDCCHregion. In a certain subframe in which a control channel for a UE whichis not located is transmitted in a PDCCH region, a starting OFDM symbolof a PDSCH indicated by CFI2 should be identical to a starting OFDMsymbol of a PDSCH indicated by the CFI. Otherwise, the UE ignores CFI2.In other words, a PDSCH is received from the eNB by applying only theCFI to a subframe in which a control channel for an idle UE, that is, aUE receiving a paging channel is transmitted. If the second method isused, a subframe in which the eNB and the UE should perform thisoperation is fixed or indicated to the UE by higher layer signaling, asin the above example.

FIGS. 9 and 10 illustrate mapping of a PDSCH to REs according to anembodiment of the present invention.

Referring to FIG. 9, when a PDSCH is mapped to REs, the PDSCH is mappedto allocated resources in a PDSCH region in a conventional manner andthen to allocated resources in a PDCCH region. The RE mapping isperformed in the first OFDM symbol of an allocated resource area alongthe frequency axis and then the same RE mapping is repeated in the nextOFDM symbol. For example, a PDSCH is mapped to REs in OFDM symbols 3 to13 and then to REs in OFDM symbol 2, as illustrated in FIG. 9. That is,the PDSCH is mapped to REs first in the PDSCH region indicated by theconventional CFI. If the CFI is different from CFI2, the PDSCH isadditionally mapped to REs, starting from the start of a PDSCH regionindicated by CFI2 in a circular manner. Accordingly, if mapping isperformed in the manner illustrated in FIG. 9, an existing buffer maystill be used.

Referring to FIG. 10, when a PDSCH is mapped to REs, the RE mappingstarts from a starting symbol of a PDCCH region and then is performed ina conventional PDSCH region. The RE mapping is performed in the firstOFDM symbol of an allocated resource area along the frequency axis andthe same RE mapping is repeated in the next OFDM symbol.

Therefore, the RE mapping of a PDSCH according to the present inventioninvolves mapping according to the conventional CFI (1) and then mappingstarting from a starting OFDM symbol indicated by CFI2 (2). Or asillustrated in FIG. 10, the RE mapping may be performed starting fromthe starting OFDM symbol indicated by CFI2. The mapping rules of FIGS. 9and 10 are the same in terms of performance such as interference andselected by the eNB.

The UE is already aware of the starting position of a PDSCH regionaccording to the CFI or CFI2 and receives information about REs mappedaccording to the mapping rules of FIGS. 9 and 10.

FIG. 11 is a block diagram of a BS and a UE which may be applied to anembodiment of the present invention.

The UE may operate as a transmitter on a UL and as a receiver on a DL.In contrast, the BS may operate as a receiver on the UL and as atransmitter on the DL.

Referring to FIG. 11, a wireless communication system includes a BS 110and a UE 120. The BS 110 includes a processor 112, a memory 114, and aRadio Frequency (RF) unit 116. The processor 112 may be configured toperform procedures and/or methods proposed by the present invention. Theprocessor 112 may control the RF unit 116 to transmit first CFIinformation indicating the number of OFDM symbols available for PDCCHtransmission. Or the processor 112 may be configured to control the RFunit 116 to transmit second CFI information indicating a starting ofOFDM symbol available for PDSCH transmission corresponding to anE-PDCCH. Or the processor 112 may control the RF unit 116 to transmit aPDSCH to the UE 120 using the first CFI information and the second CFIinformation. Herein, the PDCCH may reside in a PDCCH region of a DLsubframe and the E-PDCCH may reside in a PDSCH region of the DLsubframe. Or the processor 112 may be configured to control the RF unit116 to transmit the first CFI information to the UE 120 by RRC signalingand to transmit the second CFI information to the UE by RRC signaling orthe E-PDCCH. Or the processor 112 may control the RF unit 116 totransmit a PDSCH to the UE only based on the first CFI information in asubframe carrying a control channel to an idle UE. Herein, the secondCFI information indicates the number of OFDM symbols decreased relativeto the first CFI information. The memory 114 is connected to theprocessor 112 and stores various types of information related to theoperations of the processor 112. The RF unit 116 is connected to theprocessor 112 and transmits and/or receives a radio signal. The UE 120includes a processor 122, a memory 124, and an RF unit 126. Theprocessor 122 may be configured to perform procedures and/or methodsproposed by the present invention. The processor 122 may control the RFunit 126 to receive, from the eNB 110, first CFI information indicatingthe number of OFDM symbols available for PDCCH transmission. Or theprocessor 122 may be configured to control the RF unit 126 to receive,from the eNB 110, second CFI information indicating a starting OFDMsymbol available for PDSCH transmission corresponding to an E-PDCCH. Orthe processor 122 may control the RF unit 126 to receive a PDSCH fromthe eNB 110 using the first CFI information and the second CFIinformation. Or the processor 122 may be configured to control the RFunit 116 to receive the first CFI information from the eNB 220 by RRCsignaling and to receive the second CFI information from the eNB 220 byRRC signaling or the E-PDCCH. Or the processor 122 may control the RFunit 126 to receive a PDSCH from the eNB 220 only based on the first CFIinformation in a subframe carrying a control channel to an idle UE. Thememory 124 is connected to the processor 122 and stores various types ofinformation related to the operations of the processor 122. The RF unit126 is connected to the processor 122 and transmits and/or receives aradio signal. The BS 110 and/or the UE 120 may have a single antenna ormultiple antennas.

The embodiments of the present invention described above arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It is obvious tothose skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim by asubsequent amendment after the application is filed.

The embodiments of the present invention may be achieved by variousmeans, for example, hardware, firmware, software, or a combinationthereof. In a hardware configuration, the methods according to exemplaryembodiments of the present invention may be achieved by one or moreApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, an embodiment of the presentinvention may be implemented in the form of a module, a procedure, afunction, etc. Software code may be stored in a memory unit and executedby a processor. The memory unit is located at the interior or exteriorof the processor and may transmit and receive data to and from theprocessor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

INDUSTRIAL APPLICABILITY

The present invention may be used for a UE, an eNB, or other equipmentin a wireless communication system. Specifically, the present inventionmay be used in a multi-node system that provides a communication serviceto a UE through a plurality of nodes.

1. A method for receiving a downlink data channel from a base station ata user equipment in a wireless communication system, the methodcomprising: receiving the downlink data channel in a subframe comprisinga plurality of symbols from the base station, wherein, if the downlinkdata channel is scheduled by a first downlink control channel, astarting symbol of the downlink data channel in the subframe isconfigured by a value carried via a physical control format indicatorchannel, wherein, if the downlink data channel is scheduled by a seconddownlink control channel, the starting symbol of the downlink datachannel in the subframe is configured by a higher layer parameter. 2.The method of claim 1, wherein, if the downlink data channel isscheduled by the second downlink control channel, a starting symbol ofthe second downlink control channel is same with the starting symbol ofthe downlink data channel.
 3. The method of claim 1, wherein the valuecarried via the control format indicator channel indicates a number ofsymbols for the first downlink control channel.
 4. The method of claim1, wherein an index of the starting symbol of the downlink data channelscheduled by the second downlink control channel is less than or equalto an index of the starting symbol of the downlink data channelscheduled by the first downlink control channel.
 5. A method fortransmitting a downlink data channel to a user equipment at a basestation in a wireless communication system, the method comprising:transmitting the downlink data channel in a subframe comprising aplurality of symbols to the user equipment, wherein, if the downlinkdata channel is scheduled by a first downlink control channel, astarting symbol of the downlink data channel in the subframe isconfigured by a value carried via a physical control format indicatorchannel, wherein, if the downlink data channel is scheduled by a seconddownlink control channel, the starting symbol of the downlink datachannel in the subframe is configured by a higher layer parameter. 6.The method of claim 5, wherein, if the downlink data channel isscheduled by the second downlink control channel, a starting symbol ofthe second downlink control channel is same with the starting symbol ofthe downlink data channel.
 7. The method of claim 5, wherein the valuecarried via the control format indicator channel indicates a number ofsymbols for the first downlink control channel.
 8. The method of claim5, wherein an index of the starting symbol of the downlink data channelscheduled by the second downlink control channel is less than or equalto an index of the starting symbol of the downlink data channelscheduled by the first downlink control channel.
 9. A user equipment ina wireless communication system, the user equipment comprising: a RadioFrequency (RF) module; and a processor for controlling the RF module toreceive a downlink data channel in a subframe comprising a plurality ofsymbols from a base station, wherein, if the downlink data channel isscheduled by a first downlink control channel, a starting symbol of thedownlink data channel in the subframe is configured by a value carriedvia a physical control format indicator channel, wherein, if thedownlink data channel is scheduled by a second downlink control channel,the starting symbol of the downlink data channel in the subframe isconfigured by a higher layer parameter.
 10. The user equipment of claim9, wherein, if the downlink data channel is scheduled by the seconddownlink control channel, a starting symbol of the second downlinkcontrol channel is same with the starting symbol of the downlink datachannel.
 11. The user equipment of claim 9, wherein the value carriedvia the control format indicator channel indicates a number of symbolsfor the first downlink control channel.
 12. The user equipment of claim9, wherein an index of the starting symbol of the downlink data channelscheduled by the second downlink control channel is less than or equalto an index of the starting symbol of the downlink data channelscheduled by the first downlink control channel.
 13. A base station in awireless communication system, the base station comprising: a RadioFrequency (RF) module; and a processor for controlling the RF module totransmit a downlink data channel in a subframe comprising a plurality ofsymbols to a user equipment, wherein, if the downlink data channel isscheduled by a first downlink control channel, a starting symbol of thedownlink data channel in the subframe is configured by a value carriedvia a physical control format indicator channel, wherein, if thedownlink data channel is scheduled by a second downlink control channel,the starting symbol of the downlink data channel in the subframe isconfigured by a higher layer parameter.
 14. The base station of claim13, wherein, if the downlink data channel is scheduled by the seconddownlink control channel, a starting symbol of the second downlinkcontrol channel is same with the starting symbol of the downlink datachannel.
 15. The base station of claim 13, wherein the value carried viathe control format indicator channel indicates a number of symbols forthe first downlink control channel.
 16. The base station of claim 13,wherein an index of the starting symbol of the downlink data channelscheduled by the second downlink control channel is less than or equalto an index of the starting symbol of the downlink data channelscheduled by the first downlink control channel.